Circuit breaker having means for increasing current carrying capacity

ABSTRACT

A miniature, trip-free, ambient compensated circuit breaker has improved calibration means and is particularly adapted for high current ratings. A bell crank latch, rotatably carried by manual actuating means, is normally engaged with an ambient-compensated catch for holding stationary and movable contacts in engagement to close a circuit. Current-responsive means is adapted to release the latch from the catch to open the circuit in response to an overload in the circuit. The movable contacts are mounted on a bridge member which in turn is attached to one leg of a Ushaped spring element with the other leg securely attached to the bell crank. In one embodiment, the current responsive means is calibrated by dual adjusting screws and in a second embodiment by a single adjusting screw.

United States Patent Brassard 1 Oct. 10,1972

[54] CIRCUIT BREAKER HAVING MEANS 21 Appl. No.: 83,913

[52] US. Cl. ..337/74, 337/84, 337/101, 337/111 [51] Int. Cl. ..H0lh71/16, HOlh 73/30 [58] Field of Search... ..337/70, 71, 72, 73, 74, 75,337/76, 77, 78, 79, 80, 81, 82, 83, 84, 104, 111, 373, 375, 99, 101, 63,57, 347, 360,

2,418,537 4/1947 Wood ..337/84 Primary Examiner-Bernard A. GilheanyAssistant ExaminerDewitt M. Morgan Attorney-Harold Levine, Edward J.Connors, Jr., John A. Haug, James P. McAndrews and Gerald B. Epstein l57] ABSTRACT A miniature, trip-free, ambient compensated circuit breakerhas improved calibration means and is particularly adapted for highcurrent ratings. A bell crank latch, rotatably carried by manualactuating means, is normally engaged with an ambient-compensated catchfor holding stationary and movable contacts in engagement to close acircuit. Current-responsive means is adapted to release the latch fromthe catch to open the circuit in response to an overload in the circuit.

4 37 379 The movable contacts are mounted on a bridge member which inturn is attached to one leg of a U- [56] References Cited shaped springelement with the other leg securely at- UNITED STATES PATENTS tached tothe bell crank. ln one embodiment, the current responsive means iscalibrated by dual adjusting 3,361,882 H1968 Clarke Screws and i aSecond embodiment y a Single j 2,122,693 7/1938 Maseng ..337/70 mg Screw3,265,835 8/1966 Wood ..337/63 1,966,444 7/1934 Guett ..337/71 X 12Claims, 5 Drawing Figures 96 74 FT 102 I6 90 68 a4 18 I .92\ I04 22miminummmz I 3.697.915

' sum 1 UP 2 In ven tor, Theodore Brassard,

Att y.

PATENTEDBBT 10 m2 3.697.91 5 SHEET 2 0F 2 In van tar,

Thcodore Brassard,

CIRCUIT BREAKER HAVING MEANS FOR INCREASING CURRENT CARRYING CAPACITYThis invention relates to circuit breakers, and more particularly, to anew and improved circuit breaker of the thermostatic type forapplications in which it is desired to interrupt an electrical circuitunder predetermined conditions. Circuit breakers of the type describedin U.S. Pat. No. 3,361,882 have found wide acceptance in the marketplace and are very effective for many applications, however, theirusefulness is limited to relatively low current ratings, e.g., 20amperes or below. I

It is an object of this invention to provide a new and improved circuitbreaker particularly suitable for relatively high current ratings, e.g.,up to 35 amperes and higher, for protection of electrical circuitcomponents against excessive transients, sustained overloads, and shortcircuits; to provide a circuit breaker of the class described which isfully trip-free; to provide such a circuit breaker which is snap acting;to provide such a circuit breaker which is easily calibrated andadjusted for automatic operation; to provide such a circuit breakerwhich indicates when it is in the tripped condition; to provide such acircuit breaker which can be used as a manually operated switch withoutdeleterious effects on its function of responding properly to overloadcurrents; to provide such a circuit breaker for relatively high currentratings having increased contact forces; to provide such a circuitbreaker which is economical to manufacture and is readily adapted tomass production; and especially to provide such a circuit breaker whichis of small size, light weight, and exceedingly compact construction.

Other objects and advantages of the novel and improved circuit breakerof this invention appear in the following detailed description of twopreferred embodiments of the invention.

The invention accordingly comprises the elements and combinations ofelements, features of construction and arrangements of parts which willbe exemplified in the structures hereinafter described and the scope ofthe application of which will be indicated in the appended claims.

In the accompanying drawings in which several of the various possibleembodiments of the invention are illustrated:

FIG. 1 is a partial elevation of a circuit breaker made in accordancewith the invention with the front half of the casing removed and withthe contacts in the disengaged or open circuit position;

FIG. 2 is a partial elevation of a circuit breaker similar to FIG. 1,but with the contacts in the engaged or closed circuit position;

FIG. 3 is a perspective view of the current responsive means and dualcalibrating screws depicted in FIGS. 1 and 2;

FIG. 4 is a perspective view of the movable contact assembly used in thecircuit breaker; and

FIG. 5 is a partial elevation of a second embodiment of a circuitbreaker with the front half casing removed, and the embodiment employingan alternate calibration means.

The dimensions of certain of the parts as shown in the drawings may havebeen modified or exaggerated for the purpose of clarity of illustration.

Referring now to the drawings, and more particularly to FIGS. 1 to 4,one embodiment of this invention takes the form of a thermostatic singlephase circuit breaker (although equally applicable to multiphase circuitbreakers) generally indicated by reference numeral 10 and includes ahousing which may be formed of two shells or halves to facilitateassembly thereof. A back casing half 12 cooperates with a similar frontcasing half which has been removed for the purpose of illustration, andmay be made of any suitably strong, insulating and arc-resistantmaterial or the like. A compartment 14 is defined in the casing andreceives therein ambient compensation assembly 16 which includes anelongated catch member 18 attached at its lower end to a compensatingbimetallic member 20 and a catch return spring 22. A motion transferplate 24 is slidably mounted in the casing and is adapted to transfermotion from a current responsive bimetallic trip arm 26 to the ambientcompensation assembly 16.

As best seen in FIG. 3, trip arm 26 is generally U- shaped having distalleg portions which arebrazed to tab portions 28 and 30 of terminal 32and stationary contact arm 40 respectively. Terminal 32 also is providedwith platform 34 and slot 36 which cooperate with the casing for firmlylocking the terminal in its intended location. A notch is provided interminal 32 just below tab portion 28 to facilitate calibration in amanner to be explained below. Stationary contact arm 40, opposite tabportion 30, is provided with another upstanding portion 42 on its distalend which mounts stationary contact 44. Another stationary contact 46 ismounted on portion 48 of terminal 50.

Calibration screws 52,54 are inserted in apertures provided in the sidewall of the casing and are threaded in plates 56, 58 respectively.Plates 56, 58 are slidably inserted between bosses 60 and 62 formed inthe cas- Latch plunger is one part of the manual actuating means and ismovable between a first open .circuit switch position and a secondclosed circuit position as indicated in FIGS. 1 and 2 respectively.Since any suitable manual actuating means can be employed with theinstant invention and since it does not relate to the invention per se,details of the manual actuating means have not been shown, but referencemay be had to U.S. Pat. No. 3,361,882 referred to supra, for a completedescription of one such suitable actuating means. Latch plunger 70mounts pin 72 which in turn pivotally mounts movable contact assembly74, the main elements of which comprise bell crank latch 76, movablecontact spring 78 and contact bar 80. Bell crank latch 76 is providedwith bore 82 which receives pin 72 in plunger 70 and is movabletherewith. Another bore 84 is provided in bell crank latch 76 to permitattachment of one end 86 of spring 88, The other end 90 of spring 88 isattached to pin 92 mounted in the wall of casing 12. It will be notedthat spring 88 places a clockwise torque on bell crank 76 as viewed inFIGS. 1 and 2 tending to rotate bell crank 76 about pin 72. Bell crank76 is also provided with tongue or latch 94 which contacts catch 18 insuch a way that further clockwise rotation of bell crank 76 is precludedas long as the catch 18 remains in the position shown. Contact spring 78is secured to bell crank 76 by means of angle brackets 96 on oppositefaces of the bell crank. As seen in FIG. 4,

cutout portion 98 is provided in contact spring 78 to permit insertionof bell crank 76. Contact spring 78 is bent back on itself in a U-shapedconfiguration and is retained by lip 100 on bell crank 76. Thus, asplunger 70 is forced downwardly when latch 94 contacts catch 18, acounterclockwise torque is placed on the contact assembly 74. In theFIG. 2 contacts closed position, lip 100 separates from the contactspring 78 so that spring 78 will provide an effective contact force. Inorder to stiffen contact spring 78, ribs 102, 104 are located on the legportions. Use of brackets 96 and ribs 102, 104 provide increased contactforce which is required due to the increased instantaneous let-throughcurrents to which the circuit breaker is subjected under short circuitfault condition compared to prior art breakers referenced above. Thatis, the electrodynamic repulsion forces at the contact faces increase ina higher current rating device due to the higher let-through currents.Insulating mat 106 is mounted on that portion of contact spring 78 whichis contiguous to the contact area to preclude damage to the spring inthe event of arcing. A mechanical connection is effected between contactspring 78 and contact bar 80 as by upsetting several projections fromthe contact bar which are received in mating apertures in the springplate and headed over. Contacts 114, 116 are brazed to tab portions 110,108 respectively of contact bar 80. Stop wall 118 is provided in casing12 to limit the motion of contact bar 80 in the open contacts direction.

Electrical current passes through the circuit breaker from terminal 32through trip arm 26, stationary contact arm 40, contact 44, movablecontact 114, contact bar 80, movable contact 116, contact 46 to terminal50. As mentioned above, trip arm 26 is composed of bimetal and functionsas a current sensitive element since the electrical current passingtherethrough will cause it to heat up with the bight portion deflectingto the right as viewed in FIGS. 1 and 2 upon increasing temperature. Itwill be seen that as the bight portion of arm 26 deflects apredetermined distance it will contact motion transfer plate 24 andcontinued deflection will be transferred through plate 24 to displaceambient compensation assembly 16 until latch 94 of bell crank 76 is nolonger held by catch 18. When latch 94 clears catch 18, bell crank 76 ispivoted clockwise about pin 72 under the action of spring 88 therebydisengaging the contacts and opening the electrical circuit.

The circuit breaker is calibrated by biasing tabs 28 and 30 viacalibrating screws 52, 54 respectively. As tabs 28 and 30 are bent, thedistance between the bight portion of trip arm 26 and transfer plate 24is diminished thereby decreasing the distance trip arm 26 has to travelbefore the circuit breaker is tripped to open the circuit. Twocalibrating screws are employed since terminal 32 is relatively massiveto attain the low conductivity required for the designed high ampereratings. Therefore, the circuit breaker is designed so that neitherexcessive force nor relatively complicated configuration will berequired which would result if a single calibrating member wereemployed. Notch 38 is provided below tab 28 to facilitate thisoperation. The dual calibration screws also permit maintaining thealignment of trip arm 26 in its calibrated position, that is it affordsthe ability to more easily prevent the trip arm 26 from going askew andpossibly binding against the casing side walls.

As mentioned above, the circuit breaker is designed for especially highcurrent levels through the use of several design features. Theterminals, stationary contact arm and movable contact bar are all madeof relatively thick, massive, low-conductivity materials, trip arm 26 isjoined to tabs 28, 30 by brazing as are all of the contacts to theirsupporting structure so that no high resistance spots will occur in thecurrent path. Further, contact force has been increased withoutdiminishing operating forces.

As seen in FIG. 4, contact spring 78 is securely attached to bell crank76 by right angle members 96 on both sides of the bell crank on the legof the U-shaped spring member 78 removed from the contact bar 80. Thisattachment may be effected by welding since spring 78 does not form apart of the current path. When the contacts are in the engaged, circuitsclosed position, a force is applied through member 70, as indicated bythe arrow in FIG. 2, downwardly on bell crank 76 through bracket 96 tocontact spring 78 to apply a high force on the contacts through contactbar 80. In this position, lip 100 of bell crank 76 separates slightlyfrom the contact bar and that portion of spring 78 contiguous thereto.As soon as latch 94 separates from catch 18 and bell crank 76 pivotsclockwise tongue 100 applies a direct force against the contact bar tocause the contacts to separate and assists opening should a contact weldoccur. Ribs 102, 104 are provided in the contact spring, in addition tobrackets 96, to prevent buckling thereof with concomitant loss of springforce. Securing contact spring 78 to the bell crank 76 by brackets 96intermediate the bight portion and the end of one of the legs results ina high contact force when the contacts are in the closed circuitposition as well as providing in cooperation with lip 100 a stiff memberto facilitate opening of the contacts, particularly if a contact weldshould occur.

As described in U.S. Pat. No. 3,361,882 referenced above, ambientcompensation is provided by assembly 16. Upon heating due to the changesin ambient temperature, the end of bimetal compensating member 20 willmove to the right approximately the same distance that the bight portionof trip arm 26 moves to the right under the influence of the sameambient temperature and thus the relative spacing between these tworespective ends will remain constant. This means that in order to tripat a given electric current level, the bight portion of arm 26 mustalways deflect the same distance in order to move the bimetalcompensating member 20 a sufficient distance to trip latch 94 from catch18. The end of compensating member 20 can move under influence ofambient temperature without substantially affecting the position ofcatch 18'.

The device is so-called trip-free since if plunger 70 is held inwardlyof the casing by externally applied force, and the trip arm 26 moves tothe right (as seen in FIGS. 1 and 2) to move the ambient compensationmember 20 to the right and thus free latch 94 from catch 18, then, eventhough pin 72 is held stationary, the tension spring 88 will act on thebell crank to pivot it clockwise to pull movable contacts 114, 116 fromstationary contacts 44, 46.

FIG. 5 depicts a second embodiment of this invention in which thecircuit breaker is calibrated by a single calibration screw mountedcentrally on the bight portion of U-shaped trip arm 26. A nut mayconveniently be attached to trip arm 26 to provide screw threads foradjustably mounting screw 132. A plate 124 is mounted on plate 24 in areceiving aperture 126 and presents a downwardly extending tab 128aligned with screw 132. Aperture 122 is provided in casing 12 to permitaccess to screw 132. Once the device is calibrated, sealing compound 134may be placed about the head of screw 132 to lock it in position.Alternatively, rather than employing plate 124, a radially extendingflange may be provided in the end of screw 132 which will cooperate withmotion transfer plate 24. This embodiment is well suited forparticularly high current rating devices in which the trip arm, designedfor high current levels, is sufficiently massive and stiff thatcontacting screw 132 with a tool and turning it will not cause anydeflection of the trip arm itself upsetting the calibration thereof.

It will be appreciated that the single calibration means could beprovided equally well on the opposite side of plate 24 to cooperate withcompensating bimetallic member or on member 20 itself.

It will be seen that by means of this invention, a circuit breaker isprovided which is compact, reliable, easily calibrated and particularlysuited for relatively high current ratings.

It should be understood that although particular embodiments of thecircuit breaker have been described by way of illustration, thisinvention includes all modifications and equivalents thereof fallingwithin the scope of the appended claims.

lclaim:

1. A circuit breaker comprising:

a casing;

stationary contact means mounted in the casing;

movable contact means movably mounted in the casing and movable into andout of engagement with the stationary contact means;

overcurrent means mounted in the casing including a catch movable from alatch retaining position to a latch releasing position upon occurrenceof overcurrent conditions;

the movable contact means including a latch engageable with the catch;manual actuating means operatively connected to the movable contactmeans to move the movable contact means into engagement with thestationary contact means upon actuation of the actuating means when thelatch engages with the catch;

ambient compensation means mounted in the casing offsetting movement inthe overcurrent means due to changes in ambient temperature;

the overcurrent means including a substantially U- shaped thermostaticmember having two distal leg portions connected by a bight portion, thebight portion operatively connected to the catch, the bight portionmovable to cause movement of the catch, terminal means including twoupstanding mounting tabs separately supported in the casing, each tabhaving first and second surfaces on opposite sides thereof, the twodistal leg portions attached to respective tab portions on said firstsurfaces and camming means mounted in the casing to cam the said secondsurfaces to adjust the effective position of the bight portion of thethermostatic member to thereby calibrate the circuit breaker.

2. A circuit breaker according to claim 1 in which the camming means toadjust the effective position of the bight portion of the thermostaticmember include separate threaded members mounted in the casing alignedwith the two upstanding mounting tabs.

3. A claim according to claim 2 in which the thermostatic member isbrazed to the tab portions.

4. Overcurrent means according to claim 1 in which one mounting tab isformed from a main terminal and the other mounting tab has a legextending therefrom, the leg having a distal end for mounting thereon astationary contact.

5. A claim according to claim 1 in which the operative connectionbetween the bight portion of the thermostatic member and the catchincludes a motion transfer plate slidably mounted in the circuit breakerto transfer motion from the thermostatic member to the catch.

6. A circuit breaker according to claim 1 in which the movable contactmeans includes a spring plate bent back upon itself in a generallyU-shaped configuration having a bight portion joining two legs, at leastone movable contact supported on an end of one of the legs; and a cutoutsection formed in the bight portion, the latch made in the form of abell crank and located partially within the cutout section, and meansfixedly attaching the bell crank to the other leg of the spring plate.7. A circuit breaker according to claim 6 in which the bell crank isattached to the other leg of the spring plate intermediate the end ofthe leg and the bight portion.

8. A circuit breaker according to claim 6 in which the means fixedlyattaching the bell crank to the other leg of the spring plate comprisetwo L-shaped brackets located on opposite sides of the bell crank.

9. A circuit breaker according to claim 6 in which the movable contactmeans further includes an elongated contact bar having two ends, contactseats extending from each end, a contact mounted on each contact seat,the bell crank formed with a lip portion, the spring plate biasing thecontact plate toward the lip applying a force to the lip when thecontacts are out of engagement and applying a force to the contacts whenthe contacts are in engagement.

10. A claim according to claim 9 in which means are provided to stiffenboth legs of the spring plate.

11. A circuit breaker comprising: a casing; stationary contact meansmounted in the casing; movable contact means movable into and out ofengagement with the stationary contact means;

overcurrent means mounted in the casing including an overcurrent sensormovable upon occurrence of overload conditions, a catch, and a motiontransfer member mounted between the sensor and the catch, the motiontransfer member transferring motion from the sensor to the catch;

the movable contact means including a bell crank having a latchengageable with the catch;

manual actuating means operatively connected to the movable contactmeans to move the movable contact means into engagement with thestationary contact means upon actuation of the actuating means when thelatch engages with the catch;

the overcurrent sensor including a substantially U- shaped thermostaticmember having two distal leg portions connected by a bight portion, thebight portion movable to cause movement of the catch through the motiontransfer member, terminal means including two upstanding mounting tabsseparately supported in the casing, each tab having first and secondsurfaces on opposite sides thereof, the two distal leg portions attachedto respective tab portions on said first surfaces;

camming means mounted in the casing to cam the said second surfaces toadjust the effective spacing between two members of the overcurrentmeans to calibrate the circuit breaker;

the movable contact means further including a spring plate bent backupon itself in a generally U-shaped configuration having a bight portionjoining two legs, at least one contact supported on an end of one of thelegs; and

a cutout section formed in the bight portion of the spring platereceiving the bell crank, the bell crank fixedly attached to the otherleg of the spring plate, the bell crank formed with a lip portionlimiting movement of the spring plate maintaining the spring understress.

12. A circuit breaker comprising:

a casing;

stationary contact means including at least one stationary contactmounted in the casing;

movable contact means including at least one movable contact movablymounted in the casing and movable into and out of engagement with'thestationary contact;

actuating means mounted in the casing and including a manually movablemember and a bell crank connected to the manually movable member, thebell crank operatively connected to the movable contact means so thatactuation of the actuating means will cause movement of the bell crankand at least a portion of the movable contact means;

return spring means attached to the movable contact means to move themovable contact out of engagement with the stationary contact;

the movable contact means including a spring plate bent back upon itselfin a generally U-shaped configuration having a bight portion joining twolegs, a contact bar mounting the movable contact supported on an end ofone of the legs; and

the bight portion of the spring plate formed with a cutout section whichreceives the bell crank, the bell crank attached to the other leg of thespring plate, the bell crank formed with a lip portion extending over aportion of the contact bar to limit the movement of the spring platethereby maintaining the spring plate under stress whereby when thecontacts are in engagement the contact pressure is increased by the biasapplied by the spring plate and upon disengagement of the contactscontact welds will tend to be broken by the transfer of force from thereturn spring through the lip to the contact bar effectively bypassingthe spring plate, and means to prevent loss of contact pressure due tobuckling of the spring plate, said means including stiffening means anda permanent connection between the bell crank and the other leg.

1. A circuit breaker comprising: a casing; stationary contact meansmounted in the casing; movable contact means movably mounted in thecasing and movable into and out of engagement with the stationarycontact means; overcurrent means mounted in the casing including a catchmovable from a latch retaining position to a latch releasing positionupon occurrence of overcurrent conditions; the movable contact meansincluding a latch engageable with the catch; manual actuating meansoperatively connected to the movable contact means to move the movablecontact means into engagement with the stationary contact means uponactuation of the actuating means when the latch engages with the catch;ambient compensation means mounted in the casing offsetting movement inthe overcurrent means due to changes in ambient temperature; theovercurrent means including a substantially U-shaped thermostatic memberhaving two distal leg portions connected by a bight portion, the bightportion operatively connected to the catch, the bight portion movable tocause movement of the catch, terminal means including two upstandingmounting tabs separately supported in the casing, each tab having firstand second surfaces on opposite sides thereof, the two distal legportions attached to respective tab portions on said first surfaces andcamming means mounted in the casing to cam the said second surfaces toadjust the effective position of the bight portion of the thermostaticmember to thereby calibrate the circuit breaker.
 2. A circuit breakeraccording to claim 1 in which the camming means to adjust the effectiveposition of the bight portion of the thermostatic member includeseparate threaded members mounted in the casing aligned with the twoupstanding mounting tabs.
 3. A claim according to claim 2 in which thethermostatic member is brazed to the tab portions.
 4. Overcurrent meansaccording to claim 1 in which one mounting tab is formed from a mainterminal and the other mounting tab has a leg extending therefrom, theleg having a distal end for mounting thereon a stationary contact.
 5. Aclaim according to claim 1 in which the operative connection between thebight portion of the thermostatic member and the catch includes a motiontransfer plate slidably mounted in the circuit breaker to transfermotion from the thermostatic member to the catch.
 6. A circuit breakeraccording to claim 1 in which the movable contact means includes aspring plate bent back upon itself in a generally U-shaped configurationhaving a bight portion joining two legs, at least one movable contactsupported on an end of one of the legs; and a cutout section formed inthe bight portion, the latch made in the form of a bell crank andlocated partially within the cutout section, and means fixedly attachingthe bell crank to the other leg of the spring plate.
 7. A circuitbreaker according to claim 6 in which the bell crank is attached to theother leg of the spring plate intermediate the end of the leg and thebight portion.
 8. A circuit breaker according to claim 6 in which themeans fixedly attaching the bell crank to the other leg of the springplate comprise two L-shaped brackets located on opposite sides of thebell crank.
 9. A circuit breaker according to claim 6 in which themovable contact means further includes an elongated contact bar havingtwo ends, contact seats extending from each end, a contact mounted oneach contact seat, the bell crank formed with a lip portion, the springplate biasing the contact plate toward the lip applying a force to thelip when the contacts are out of engagement and applying a force to thecontacts when the contacts are in engagement.
 10. A claim according toclaim 9 in which means are provided to stiffen both legs of the springplate.
 11. A circuit breaker comprising: a casing; stationary contactmeans mounted in the casing; movable contact means movable into and outof engagement with the stationary contact means; overcurrent meansmounted in the casing including an overcurrent sensor movable uponoccurrence of overload conditions, a catch, and a motion transfer membermounted between the sensor and the catch, the motion transfer membertransferring motion from the sensor to the catch; the movable contactmeans including a bell crank having a latch engageable with the catch;manual actuating means operatively connected to the movable contactmeans to move the movable contact means into engagement with thestationary contact means upon actuation of the actuating means when thelatch engages with the catch; the overcurrent sensor including asubstantially U-shaped thermostatic member having two distal legportions connected by a bight portion, the bight portion movable tocause movement of the catch through the motion transfer member, terminalmeans including two upstanding mounting tabs separately supported in thecasing, each tab having first and second surfaces on opposite sidesthereof, the two distal leg portions attached to respective tab portionson said first surfaces; camming means mounted in the casing to cam thesaid second surfaces to adjust the effective spacing between two membersof the overcurrent means to calibrate the circuit breaker; the movablecontact means further including a spring plate bent back upon itself ina generally U-shaped configuration having a bight portion joining twolegs, at least one contact supported on an end of one of the legs; and acutout section formed in the bight portion of the spring plate receivingthe bell crank, the bell crank fixedly attached to the other leg of thespring plate, the bell crank formed with a lip portion limiting movementof the spring plate maintaining the spring under stress.
 12. A circuitbreaker comprising: a casing; stationary contact means including atleast one stationary contact mounted in the casing; movable contactmeans including at least one movable contact movably mounted in thecasing and movable into and out of engagement with the stationarycontact; actuating means mounted in the casing and including a manuallymovable member and a bell crank connected to the manually movablemember, the bell crank operatively connected to the movable contactmeans so that actuation of the actuating means will cause movement ofthe bell crank and at least a portion of the movable contact means;return spring means attached to the movable contact means to move themovable contact out of engagement with the stationary contact; themovable contact means including a spring plate bent back upon itself ina generally U-shaped configuration having a bight portion joining twolegs, a contact bar mounting the movable contact supported on an end ofone of the legs; and the bight portion of the spring plate formed with acutout section which receives the bell crank, the bell crank attached tothe other leg of the spring plate, the bell crank formed with a lipportion extending over a portion of the contact bar to limit themovement of the spring plate thereby maintaining the spring plate understress whereby when the contacts are in engagement the contact pressureis increased by the bias applied by the spring plate and upondisengagement of the contacts contact welds will tend to be broken bythe transfer of force from the return spring through the lip to thecontact bar effectively bypassing the spring plate, and means to preventloss of contact pressure due to buckling of the spring plate, said meansincluding stiffening means and a permanent connection between the bellcrank and the other leg.